Starburst galaxies

Paul P. van der Werf

Principal collaborators: A. Moorwood, E. Oliva, F. Israel

Overview:

Starburst galaxies form stars at such a high rate that that, given their available gas reservoir, this star formation rate would be sustainable only for a timescale much shorter than the Hubble time. Starbursts are therefore transient phenomena. During a starburst episode a galaxy undergoes rapid evolution in colour, morphology, gas and dust content, metallicity and stellar population. Since starbursts can be triggered by merging, and merging is an important mechanism of galaxy evolution, starbursts are of central importance ingalaxy evolution. Some starbursts are accompanied by a superwind or an active galactic nucleus. My main interests are the properties of stars and gas in nearby (circum)nuclear starbursts as probed in the near- and mid-infrared (e.g., NGC253 and NGC1808), ultraluminous infrared galaxies, the role of starbursts in galaxy evolution.

Highlights:

Spatial structure and evolution of starbursts: Since starbursts are dusty, infrared observations are needed to probe them. The near-infrared region contains bright spectral features that each probe different phases of the starburst: hydogen and helium recombination lines probe the upper main sequence, [FeII] 1.64 and 1.26 µm emission lines trace shocks from supernova remnants, H₂ vibrational lines trace the hot molecular gas in the starburst region, and the K-band continuum is (usually) dominated by red supergiants, with bright spectral features such as the CO absorption bands. Spatially resolved spectroscopy reveals morphological details of the starburst: the star formation takes place in a number of compact complexes or super starclusters, each of which has a massive stellar content exceeding that of the most spectacular Local Group star cluster (30 Dor) by an order of magnitude. Such spatial detail in the starburst is found for instance in the nearby starbursts NGC253 and NGC1808. Morphological differences in Brγ equivalent width or Brγ/[FeII] ratio reveal different evolutionary phases of the starclusters and hence the spatial evolution of the starburst. For instance, in NGC1808, the high Brγ equivalent width in one side of the galaxy (see images below) reveals that the youngest starburst occurs on that side, while the starburst activity on the other side is more evolved.

False colour images of the nuclear region of NGC1808 in Brγ line emission (left) and K-band continuum (right).

Principal publications:

1. High resolution imaging of [FeII] 1.64 micron, Brackett γ and H₂ 1-0 S(1) emission in the starburst galaxy NGC253
   Forbes, D.A., Ward, M.J., Rotaciuc, V., Blietz, M., Genzel, R., Drapatz, S., Van der Werf, Paul P., & Krabbe, A.
   ApJ, 406, L11 (1993)
   [ ADS entry | ADS scanned paper ]

2. Starburst superwind and LINER activity in NGC4945
   Moorwood, A.F.M., Van der Werf, Paul P., Kotilainen, J.K., Marconi, A., & Oliva, E.
   A&A, 308, L1 (1996)
   [ ADS entry | ADS scanned paper | colour plate ]

3. Near-infrared line and continuum imaging of the nuclear starburst region of NGC1808
   Kotilainen, J.K., Forbes, D.A., Moorwood, A.F.M., Van der Werf, Paul P., & Ward, M.J.
   A&A, 313, 771 (1996)
   [ ADS entry | ADS scanned paper ]

See also:

Ultraluminous infrared galaxies

Galaxy evolution

Interstellar medium of nearby galaxies

Starburst links